DESCRIPTION (Taken from the Investigator's Abstract) Environmental stresses such as microorganisms and toxic chemicals have profound effects on lung injury and pulmonary disease. Airway bacterial infection has been associated with various lung diseases such as pneumonia, cystic fibrosis, and tuberculosis. Tobacco smoke (TS) is known to induce pulmonary diseases such as emphysema and lung cancer and has effects on the host defense mechanism against pathogens, but the molecular mechanisms by which this occurs is not completely understood. The long-term goal of this proposal is to investigate the functional characteristics of a novel airway specific gene, DD4, its regulation and its potential role in health and human lung diseases that relate to tobacco smoke. The human DD4 gene is specifically expressed in serous cells of submucosal glands where bactericidal proteins such as lysozyme and lactoferrin are secreted. This novel gene has exhibited significant response to promoting agents of mucous cell differentiation such as UTP and retinoids, as well as to several mediators of inflammation and proliferation such as tumor necrosis factor-alpha (TNF-alpha) and epidermal growth factor (EGF). Of potential significance, the candidate?s preliminary studies revealed that DD4 has antibacterial properties and that its secretion varied dramatically between different lung diseases. In addition, the candidate?s laboratory also observed that human DD4 MRNA expression is elevated upon TS stimulations in both time and dose dependent manner. The objective of this application is to elucidate effects of TS on the regulatory mechanism of DD4?s gene expression and to examine DD4?s function after TS exposure both in vitro and in vivo. The central hypothesis to be tested is that DD4 is a secreted bactericidal protein that plays a role in airway defense mechanisms against pathogens. The rationale behind this research is that modulation (such as TS exposure) of the secretary DD4 protein is one means of directly affecting host defense response against human airway infection. Therefore, regulation of DD4 gene expression and protein secretion in response to pathological stimuli must be understood before the mobilization of host defenses and the pathogenesis of airway diseases that are related to DD4 can be fully appreciated. To accomplish the objectives of this application, they will pursue three specific aims: (1) to characterize the bactericidal activity of DD4; (2) to elucidate the regulatory mechanism of TS exposure on DD4?s bactericidal function; (3) to evaluate DD4?s antibacterial effect in vivo. At the completion of this research, the candidate expects to have determined the bactericidal potency of DD4 and the regulation by TS of the antibacterial defense mechanism of DD4. The candidate expects that regulation of DD4 will prove to be related, at least in part, to the inflammatory response and tobacco smoke exposure. Finally, the candidate may obtain a better understanding of the pathogenesis of bacterial infections in certain lung diseases under effects of tobacco smoke, and the development of new therapeutic strategies.